IS:6280 -1971 (( Reaffirmed 2001) ) Reaffirmed 1999 Indian Standard SPECIFICATION FOR SEWAGE SCREENS ( Third Reprint NOVEMBER 1998 ) UDC 628.334.11/.12 0 Conright 1972 STANDARDS ZAFAR MARG BUREAU MANAK OF INDIAN BHAVAN, 9 BAHADUR SHAH NEW DELHI 110002 Gr 3 February 1972 Indian Standard SPECIFICATION FOR SEWAGE SCREENS Public Health Engineering Equipment Sectional Committee, BDC 40 Chaimzan SHRI A. K. ROY Reprazmting Loca~u~~f$ovemment Engineering Department, Members Shri A. K. Roy ) PROF S. J. ARCX~VALA SUPERINTENDING ENOINEER ( Alternate to Central Public Health Engineering Research Institute ( CSIR ), Nagpur Engineer-in-Chief's Branch, Army Headquarters Gee-Miller 8r Co, Calcutta SHRI D. G. BAPAT DR T. R. BHASKARAN Sriar R. N. KAR ROY ( Altematc ) All India Manufacturers' Organization, Calcutta DR B. V. BH~~TA Calcutta Metropolitan Organization, Calcutta SHRI S. CHATIZRJEB Dorr-Oliver ( India ) Ltd, Bombay SHRXN. D. CHHABRIA Public Health Engineering Department, Government CHEEPENIXNEER of Bihar DEPUTY CHIEF ENQINEER( Afrernak ) Municipal Corporation of Delhi CHXEPENGINEER ( WATER ) Bombay Municipal Corporation Crrv ENGINEER Sxm L. P. BORKAR (A&mate) Paterson Engineering Co ( India ) Pvt Ltd, Calcutta &RI S. Y. ChRB Public Health Engineering Department, Government SHRI D. R. JAOANNATH RAO of Madhya Pradesh Srmx D. V. S. MURTAY ( Altwnate ) The Hindustan .Construction Co Ltd, Bombay SHRI M. Y. MADAN All InIn$;t~nsutute of Hygmne & Pubhc Health, PROP N. tiJUMm3 SHRI S. SUBBA RAO ( AI&mob ) Department ofHealth, SHRI S. K. MAJIJMDER SWRI B. NANDY ( SHRI S. C. MA~~M~ER SHRI S. M~I-~ER Government of West Bengal Gannon Dunker1 & Co Ltd, New Delhi Corporation of C 3 cutta In E;i8ypacity ( ` U&yarn `, Shimji SHRI N. V. MODAK Al&mate ) Park, SHRI V. P. NARAYANAN NAYAR SHRXPIIRTEJSINQH REPRB~ENTATIVB REPRE~BNTAT~VB REPRESZNTATIVE Public Health Engineering Department, Government of Kerala Hindustan Steel Ltd, Bhilai Institution of Engineers ( India), CaRutta John Tmson & Co Ltd, New Delhi Ministry of Health (conlinurdoapcg~2) BUREAU MANAK OF INDIAN STANDARDS ZAFAR MARG BHAVAN, 9 BAHADUR SHAH NEW DELHI 110002 IS:6280-1971 Refiessnting RRPRESBXTATIVE SHRISAT PALSINCH SHRI D.R. SINGAL SHRI SHRI SHRI SHRI P. S. TENDOL~CAR C. L. SASTRI ( Alternate ) C. V~SWESWARAIAH Victoria Jubilee Technical Institute, Bombay Directorate General of Technical Development Public Health Engineering Department, Government of Punjab Candy Filters ( India ) Ltd, Bombay Public Health Engineering Department, Governmen& of Mysore Director General, IS1 ( Ex-o&o Member ) Secretary SHRI II. APTHA SIMHA, Director ( Civ Engg ) C. R. RAMA RAO Deputy Director ( Civ Engg ), ISI Sewage ConDefier PROP S. J. ARCEIVALA Members BR T. R. SHRI Treatment Equipment Panel, BDC 40 : P2 Research Central Public Health Engineering Institute ( CSIR ), Nagpur Geo-Miller & Co, Calcutta R. N. KAR BHA~KARAN ROY (Alternate) Alternate) SHRI N.L).CHHABRIA Snm V. D. DESAI SHRI L.P. BORKAR( SHRIM.Y.MADAN Dorr-Oliver India Ltd, Bombgy Bombay Municipal Corporation The Hindustan Construction Co Ltd, Bombay Victoria Jubilee Technical Institute, Bombay EIMCO-KCP Ltd, Madras Hydraulic & General Engineers Pvt Ltd, Bombay All India Institute of Hygiene & Public Health, Calcutta Loca~u~;fo~ment Engineering Department, PROP B. L. MAHABAL SHRI H. N. MISRA SHRI S. S. NAIK SHRI S. SUBBA RAO SUPERINTENDINGENGINEER 2 IS : 6280 - I971 Indian Standard SPECIFICATION FOR SEWAGE SCREENS 0. FOREWORD 0.1 This Indian Standard was adopted by the Indian Stanciarcis Instifll7iw! on 27 October 1971, after the draft finalized by the Public lienltll lL11~1"neering Equipment Sectional Committee had been approved by the C:i\ii Engineering Division Council. 0.2 Unsatisfactory or insanitary disposal of sewage and indrlstrial FVRO(C Treatment of sewage: IX!~JIY leads to nuisance and public health hazards. therefore, assumes much importance. 7'he eci<:ii,its ultimate dispokl, ment used in the treatment of sewage should be designed and consi~~u~:~~~~l to suit the purpose. Standards are being formulated for different typt:s of equipment used in sewage treatment. 0.3 Sewage admitted to sewage treatment plant and pumping stations should be effective& screened to protect the machinery in the plant and to avoid difficulties and unsightly conditions in subsequent stages of treatment. Screens are also necessary to intercept unsightly and repulsive floating matter where raw sewage is discharged into a water course withour Screens, mechanically or manually cleaned are normally ~scd treatment. for this purpose and this standard covers their requirements. 0.4 There is no standard design criteria for screens in the country and guidance on this aspect is basically necessary for suiting the equipment to the scheme of sewage treatment as a whole. Certain recommendatinrr-. have, therefore, been given in 0.4.1 to 0.4.3 for general guidance and t$; These design criteri,L indicate the basis of the specification themselves. will be reviewed when more data becomes available for the Sectional Committee's consideration. 0.4.1 Wherever the average quantity of sewage exceeds 400 ma/h rnrcllaAll mechanically cleaned medium scrcz11~ nical screens are recommended. should be preceded by a coarse screen which is manually screened. 0.4.2 Channels in which screening devices are to be installed should ;+ designed to provide a velocity of not less than 0.3 m/s at average dcsigr; flow. 0.4.3 The effective area of opening of the scrmn ( which is the vertica! projected area of the screen openings from the invert af the channel to the 3 IS : 6280- 1971 flowline ) should be such as to produce a velocity through the screen opening not exceeding 0.9 m/s at maximum expected flow. 0.5 For the purpose of deciding whether a particular requirement of this standard is complied with, the final value, observed or calculated, expressing the result of a test or analysis, shall be rounded off in accordance with The number of significant places retained in the rounded IS : 2-1960*. off value should be the same as that of the specified value in this standard. 1. SCOPE 1.1 This standard covers the materials, dimensions and methods of construction of screens used in treatment plants for domestic as well as municipal sewages, the latter often containing a variety of industrial wastes. 1.2 This standard shall also be applicable where screens are intended to be used. to wholly industrial wastes 1.3 The standard does not cover fine screens and communitors are not yet in common use at present in India. 2. TERMINOLOGY since these 2.0 For the purpose of this standard, the following definition shall apply. screening device comprising of flats of rectangular or 2.1 Screens -A trapezoidal section placed vertically, inclined or curved and spaced at close and equal intervals across a channel through which sewage flows. It is used for removal of certain materials such as pieces of wood, floating debris,. leaves, frigs, rags, etc, found in sewage. Depending on the clear spacing between flats, the screens shall be classified as under: a) Coarse screens Above 50 mm b) Medium screens c) Fine screens 20 to 50 mm Less than 20 mm 3. MATERIALS 3.1 The materials Table 1. 4. LOCATION devices generally precede grit chamber. Screens shall preferably be installed in open channels; where screens are required to be located in deep pits or inside buildings the precautions given in 4.1.1 and 4.1.2 shall be taken. *Rules for roundingoff numericalvalues (revised). to be used for different component parts are given in 4.1 Screening 4 ISt6280-1971 TABLE 1 MATJZRULS FOR DIFFERENT PARTS OF SEWAGE SCREENS (Cfaasr 3.1 ) SL No. CoMPoNxNTPAxTs Civil works RECOMMENDBD MATEiUU3 REP TO INDUN STANDARD IS : 456-19641 IS : 2212-19622 IS: 1597 ( Part I )-1967s Is : 1597( Part II )-I9674 IS : 3042-1965s IS : 226-1969' 3 a) Concrete b) Brick masonry c) Stone masonry a Cast iron b 1 Steel Plastic ( polycfh~lCnC, PVC, glass rem arced polyester ) a) Fabricated structural steel b) Cast iron cast steel Cold finished steel ii) iii) Gates Flaats Rake arm and Frame, Raking mechanism T&h Shaft Motors, starters, time switches, electrode switches Flats, channels Bearings S;ni ;;s, cables, chains Sheet housing Reduction gear iv) IS 226-19696 IS : 210-19627 IS : !030-19626 IS : 1570-1961s IS : 325~1961'O IS : 996-19641' IS : 1766-19611' IS : 1822-19671s IS : 226-19696 Grade 5 of IS : 318-196214 IS : 2266-19631s IS : 1730-196116 IS : 1570-19619 and IS : 1871-19651' v) vi) vii) viii) ix) x) xi) xii) Structural steel Bronze Steel Mild steel Steel U&de of practice for plain and reinforced concrete for general buildings construction ( secondr&ion ) . aCode of practice for brickwork. at&de of practice for construction of stone masonry: Part I Rubble stone masonry. &Specification for construction of stone masonry: Part II Ashlar masonry. aSpecification for single faced S~UICC. gates ( 200 to 1 200 srxe ) . aspecification for rtructural steel ( standard guahty ) (JoMth revision) . vspecification for grq iron casting ( rmismi ) . aSpecification for steel castings for general engineering purposes. ( r&cd ). @Specification for schedules for wrought steel for general engmeerrng purposes. loSpecification for three-phase inductron motors. ( sscoadrsvss~n ) . llSpeci6cation for single-pharm small ac and unrvcrsal &ctrm motors ( revised ) . laSpe&cation for time switch-. 1aSpecification for ac motor StartCm fv Voltage not exceeding 1000 volts (fist revision) . USpcci6cation for leaded tin bronze sngotr and c+np ( rewed ) . 16S~ification for steel wire ropes for general engmearng purposes. l@Spccification for dimensions for steel plate, sheet and strip and structural and general mgineking purposes. lvcommentary on Indian Standard wrought steels for g*laal engineering purposes. 5 IS : 6280 - 1971 4.1.1 Screening devices located in deep pits shall be provided with stairway access, adequate lighting, ventilation and convenient and adequate means for removing screenings. While coarse screens may need to be provided in this manner before pumps, installation of medium screens in deep pits shall be avoided due to operational and maintenance difficulties. 4.1.2 Screening devices installed in a building where other equipment or offices are located shall be separated from the rest of the building by partitions and provided with adequate means of ventilation. 5. CONSTRUCTION 5.1 General Requirements for Coarse and Medium Screens 5.1.1 The top of the screen shall be at least 300 mm above the highest flow level. 5.1.2 In manually cleaned screens, the top of the screen channel shall be provided with a perforated platform from which the operator may conveniently rake the screenings from the screen. Suitable draining facilities shall be provided in the platform. A hand rake shall be provided. 5.1.3 The screen shall be embedded in such a manner that the frame, if any, shall offer no obstruction to the flow of sewage. 5.1.4 The flat shall not be less than 10 mm in thickness 50 mm deep. The flats shall not have any joints. The the flats shall be uniform and preferably so maintained by of spacers, which shall be SO located as not to interfere operation. and not less than spacing between adequate number with the raking 5.1.5 For facility of manual cleaning of the screen inclination shall be between 45' and 60" to the horizontal. 5.1.5.1 Screens installed in deep pits may also consist of flats fixed to a suitable steel frame. Frame shall be placed freely in cast iron guide provided in the sides and bottom of the channel so as to provide no obstruction to flow of sewage and shall enable easy lifting, whenever required. For this purpose such screens are installed vertically. 5.1.5.2 The cleaning may be done by providing two coarse screens, one behind the other with independent arrangement for hauling the screen with the screenings to the surface for cleaning purposes. Such screens need to be provided with a flat plate of 300 mm width slightly inclined towards the screen at the bottom to catch the screenings during lifting operation. In case of large plants the screen channel may be suitably divided to have a maximum screen width of I.5 m. 5.1.6 Where necessary, provision should be made for adequate ventilation and lighting. The lamps should be of low-voltage and/or of flame 6 IS : 6280 - 1971 proof type. Ventilation should be of the forced type which may be provided by blowers located at ground level with suitable flexible ducting to displace out air from the pit swiftly. 5.1.7 The screen channel invert downstream of mechanically operated screen shall drop not less than 75 mm below the invert level of screen channel; in the case of manually operated screen, the drop shall be not less than 150 mm. 5.1.8 The channel preceding and following the screens shall be filletted. 5.1.9 A minimum free-board of 300 mm shall be provided; this may be suitably raised where required by turbulent conditions in the channel. 5.1.10 The design of approach channel for screens shall provide for gates to shut off flow or divert the flow to other units or bye-pass it ( see 5.2.2 ). 5.1.11 Provision of a canopy over screen platform is advisable to facilitate operation under all weather conditions. 5.1.12 Necessary approach road shall be provided from the screen to the point of disposal. to the screen and 5.1.13 All the corners shall be rounded and the edges shall be chamfered near the screen to facilitate the cleaning of [he channel near the screen. 5.2 Mechanically Cleaned Units 5.2.1 Mechanically cleaned screen shall consist of a screen provided with a mechanical raking device for cleaning operation. 5.2.2 Whenever a mechanically cleaned screen is used, an auxiliary unit either mechanically operated or manually operated shall be provided as a standby with suitable arrangements for diversion of flow. 5.2.3 The inclination of the screen shall be between 60" and 90" with the horizontal in case of straight flats. 5.2.4 The part of the screen above the platform may be kept open to facilitate inspection. 5.2.5 The screen shall be provided with a raking mechanism for removing The raking mechanism may be (a) revolvthe screenings from the screen. ing type ( for curved screen ), or (b) reciprocating type ( for straight screens which move up and down, or (c) endless revolving type. In each case rake arm teeth shall be SO formed as to mesh with the screen, throughout the period of removal of screenings. The rake speed shall not be more than 3 m/min. Typical illustration of screens are given in Fig. 1, 2 and 3. 7 IS : 6280 - 1971 @AKE RAKE SCRAPER ROCKING APRON BAR AN SCRAPER SUPPORT ARM Fro. 1 CURVED SCREEN WITH REVOLVING RAKE $?EDUCTIDN GEAR SPROCKET WHEEL CHAIN // ELECTRIC MOTOR \ SUSPENSION @/-BELTS ,/RAKfz,t,LELygG COUNTER WEIGHT \ /-CDNVEVDR BELT /-HINGE SHIELD /SCREEN _SEWAGE LEVEL RAKE / FLOW 2A Vertical Fro. Screen with Reciprocating Rake Contd 2 SCREEN WITH RECIPROCATING RAEB <8 IS:6269-1971 PAN HOPPER TURN BUCKLES RAKE GUIDE RAIL SCREEN FLOW .e SCREEN SUPPORT 28 Inclined Screen with Reciprocating Screen Fro. 2 SCREEN WITH RECIPROCATINO RAK& 9 IS:6280-1971 CL AKE FIG. 3 SCREEN WITH ENDLESS REVOLVING RAKE 5.2.6 In raking mechanisms of the revolving or reciprocating type, the size of the shaft shall be adequate but not less than 60 mm in diameter. Lower shaft sprockets shall be provided with bushings for underwater service in gritty conditions. Upper shaft sprockets shall be split facilitating replacement. The chain or cable used shall be of material having tensile strength of not less than 2 000 kgf/cm*. 5.2.7 The entire raking mechanism shall be designed to be rigid to prevent deflection and to ensure that the rack will pesh with screen at all may be provided in sections to facilitate times. A raking comb replacement. 5.2.8 The motor shall comply with the requirements specified in or IS : 996-1964t and shall be totally enclosed fan cooled type IS : 325-1961* The motor shall be not less than and suitable for outdoor mounting. 0.5 kW in capacity. The drive unit shall consist of reduction gear preferably oil immersed type with anti-friction bearings. Each motor shall be provided with magnetic starter and' no-volt and overload protection devices. The drive itself, either chain or belt type, shall be enclosed in sheet metal guard of thickness not less than 2 mm. For motors installed in the open, additional cover in the form of louvered box may be provided over the motors. A push button type control shall be provided near the motor. An additional control at a central point may be provided in the case of large plants, where desired. 5.2.9 The rake cleaning arrangement shall be such as to ensure that the screenings lifted up by mechanism are not allowed to drop back in the sewage downstream of the screen; this may be accomplished by providing *Specification for three-phase induction motors ( secondrevision) . tSpecification for single-phase small ac and universal electric motors ( rev&f ). 10 IS : 6280 - 1971 Where a dead plate is provided a dead-plate or any other suitable device. it shall be of mild steel not less than 5 mm thickness and running for the full width of the screen for retaining the screenings discharged by the rake at the discharge end. Where necessary, the removal of the screenings to a distant receptable may be made by providing a suitable belt conveyor at a required height for facilitating its loading directly into a trolley or trailer. 5.2.10 The raking mechanism shall be operated by either a time switch or an automatic float control or electrode type switch. The provision of time switch is, however, preferred because of its greater reliability. In the case of time switch the setting shall be variable to enable the operator to In the case of float set the frequency as dictated by the plant operation. controlled switch, the control shall be such that the operator may vary The float shall preferably be rod operated. An the head differential. additional electrode switch may be provided to operate the mechanism continuously at a pre-determined high level in the channel while giving a visible and audible alarm. 5.2.11 The raking mechanism shall also be provided switch for operating the rake at will. with an auxiliary 5.2.12 In addition to the overload protection devices provided to electric motors, the raking mechanism may also be provided with a mechanical type overload device which shall automatically disengage the rake, if the unit is overloaded due to an unusual obstruction or jamming of rake or some other cause. 5.2.13 To facilitate cleaning of raking equipment, conveyor belt, etc, it is recommended that a pressure pump ( to give a minimum of 2 kgf/cms ) may be provided at a suitable location. 6. PAINTING 6.1 Red,oxide ( zinc chromate ) shall be used as a primer for painting. One coat of primer and at least 3 coats of bitumastic or other approved anti-corrosion paint shall be applied after erection [ see IS : 1477 ( Part I )1959* and IS: 1477 ( Part II )-1963t]. 7. DISPOSAL, OF SCREENINGS 7.1 To facilitate collection and disposal of screenings, rubber tyred tipper of capacity not less than 140 litres may be provided; trailers may be used in the case of large plants and for small plants wheel barrows which could The disposal of screenings may be either be properly cleaned may be used. done by sanitary land fill or incineration. *Code of practice for finishing of iron and steel ferrous metal in buildings, painting and allied finishes: Part I Operations and workmanship. t&de of practice for finishing of ferrous metals in buildings, painting and allied finishes: Part II Schedules and equipment. 11 BUREAU OF INDIAN STANDARDS Headquarters: Manak Bhavan. 9 Bahadur Shah Zafar Mare, NEW DELHI 110002 Telephones: 323 0131,323 3375,323 9402 Fax : 91 11 3234062, 91 11 3239399, 91 11 3239382 Telegrams : Manaksanstha (Common to all offices) Telephone Central Laboratory : Plot No. 20/9, Site IV, Sahibabad Industrial Area, Sahibabad 201010 Regional Central *Eastern Offices: 32376 17 8-77 00 32 : Manak Bhavan.9 Bahadur Shah Zafar Marg, NEW DELHI 110002 : l/14 CIT Scheme VII M, V.I.P. Road, Maniktola, CALCUTTA 700054 160022 337 86 62 60 38 43 235 23 15 832 92 95 Northern : SC0 335-336, Sector 34-A, CHANDIGARH Southern : C.I.T. Campus, IV Cross Road, CHENNAI 600113 IWestern : Manakalaya, E9, Behind Marol Telephone Exchange, Andheri (East), MUMBAI 400093 Branch Offices:: `Pushpak', Nurmohamed Shaikh Marg, Khanpur, AHMEDABAD SPeenya Industrial Area, 1 st Stage, Bangalore-Tumkur BANGALORE 560058 Road, 380001 550 13 48 839 49 55 55 40 21 40 36 27 21 01 41 8-28 88 01 8-71 1996 Gangotri Complex, 5th Floor, Bhadbhada Road, T.T. Nagar, BHOPAL 462003 Plot No. 62-63, Unit VI, Ganga Nagar, BHUBANESHWAR Kalaikathir Buildings, 670 Avinashi Road, COIMBATORE Plot No. 43, Sector 16 A, Mathura Road, FARIDABAD Savitri Complex, 116 G.T. Road, GHAZIABAD 201001 781003 500001 751001 641037 121001 53/5 Ward No.29, R.G. Barua Road, 5th By-lane, GUWAHATI 54 11 37 201083 37 29 25 21 68 76 5-B-56C, L.N. 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